Recently, the Federal Communications Commission (FCC) has approved the operation of unlicensed radio transmitters in the broadcast television spectrum at locations where that spectrum is not being used by licensed services, such as television stations and wireless microphone operators, under certain rules. This unused TV spectrum is often termed “white space”. A concept called Cognitive Radio was proposed to implement negotiated, or opportunistic, spectrum sharing to improve spectrum efficiency for these frequencies.
It can be expected that the implementation of Cognitive Radio (CR) in TV white space will be a major topic within wireless communication into the future and provide a viable solution to the problem of scarcity of the wireless spectrum. In 2004, based on the expectation of unlicensed use of TV white space, under the charter of an IEEE 802 Standards Committee, a working group named IEEE 802.22 was established to develop a standard for a Cognitive Radio-based PHY/MAC/air interface for use by license-exempt devices on a non-interfering basis in spectrum that has already been allocated to the TV Broadcast Service. The IEEE 802.22 working group is also called the WRAN Group, since it is essentially developing an air interface for a Wireless Regional Area Network (WRAN) with a range as large as 30 miles.
An alternate idea is to standardize the use of this spectrum to provide services similar to that of the traditional IEEE 802.11 WiFi standard. This effort to use TV white space for WiFi access is known as 802.11af. The difference between the traditional 802.11 standards and 802.11 of is that 802.11 of will be for WiFi operation in the TV white spaces.
TV white space (TVWS) consists of fragments of TV channels. Thus, depending on the usage of TV broadcasting and wireless microphones, the spectrum opportunity may be 6 MHz, 12 MHz, 18 MHz, . . . assuming that a TV channel is 6 MHz wide. In addition, the spectrum opportunity may happen in any of the TV bands. Thus, the spectrum opportunity in TVWS differs from the traditional 802.11 bands of 2.4 GHz, 3.6 GHz and 5 GHz in that the center frequency and channel bandwidth are variable.
Due to the combinations of bandwidths in TVWS, and variable center frequencies, the channel access delay and the complexity in finding available bandwidth can be large. In addition, as part of the process to find available bandwidth, unlicensed 802.11 devices wishing to operate as dependent stations are subject to channel permissioning and regulatory controls. Once transmitting, these unlicensed devices need to be identifiable to a database administrator in case they cause interference to other authorized devices.